react-native-ble-plx supports scanning of BLE peripherals.

To perform a scan one must use:

bleManager.startDeviceScan(
  UUIDs: ?Array<UUID>,
  options: ?ScanOptions,
  listener: (error: ?Error, scannedDevice: ?Device) => void
)

• UUIDs—Array of strings containing UUIDs of Services which are registered in scanned Device. If null is passed, all available Devices will be scanned.
• ScanOptions—Optional configuration for scanning operation.
  • allowDuplicates?: boolean—duplicate scanning records are received more frequently [iOS only—default false]. On Android the duplicates will be emitted.
• listener—Function which will be called for every scanned Device (devices may be scanned multiple times). It's first argument is potential Error which is set to non null value when scanning failed. You have to start scanning process again if that happens. Second argument is a scanned Device

When the scan is no longer needed one must call:

bleManager.stopDeviceScan()

• iOS:
  • Background scanning—one must provide a non-empty UUIDs array and be aware of how the app behaviour will change.
• Android:
  • Since Android 6 to scan the app needs to have ACCESS_COARSE_LOCATION or ACCESS_FINE_LOCATION runtime permission. Since Android 10 only ACCESS_FINE_LOCATION is accepted by the OS.
  • Background scanning—the OS may kill the application on arbitrary moment once in the background. There are native ways of waking/keeping the app. Since Android 10 to scan in background an additional runtime permission is needed: ACCESS_BACKGROUND_LOCATION
  • Performing other BLE actions while scan is active may cause problems on some devices.